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Blog posted by: James Peacock – Developer, GOV.UK Pay, 11 July 2023 – Categories: GOV.UK Pay, Posts for Tech Specialists.

This is part of our blog series intended for a technical audience. While we try our best to explain things clearly, we will use technical terms in common use in the industry. As part of our practice of working in the open, GDS likes to write about our technical work, so that we can share and connect with technical specialists around the world.

This blog post is an experience report of conducting performance tests, highlighting the value and importance of conducting this kind of test. 

Performance testing has given us confidence that our webhooks mechanism can deal with large transaction volumes. Along the way, it helped us identify problems that had not shown up in other tests. As a result, what we deliver will be more efficient and robust. 

GOV.UK Pay is used by hundreds of services across the public sector to take payments. The GOV.UK Pay team recently released our Recurring Card Payments feature into production. An important part of this feature is the webhooks mechanism. Webhooks allow services that use Pay to receive messages about payment events, for example when a payment succeeds or fails. They can be used in a variety of ways, for example to trigger messages to a service's paying users or connect with enterprise resource planning (ERP) software to help automate accounting.

Preparing for the release, we were confident that the mechanism worked from a functional point of view, as we’ve had webhooks running in our sandbox environment for several months. However, we had never tested them under any load, and we wanted to be sure that the mechanism would cope when partner services start subscribing to webhooks.

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